1. Field of the Invention
This invention relates to an epicyclic differential gear system and more particularly to an improved steering differential capable of transmitting power and providing steering control and braking action to the driving tracks of a tracked vehicle.
2. Description of the Prior Art
Conventional steering differentials have typically provided means for transmitting power, which is delivered axially to the unit by a drive shaft from a prime mover by way of a transmission, transversely to the tracks of a vehicle. Steering and differential action is provided by overdriving an output shaft that carries power to the tracks located on the side of the vehicle away from the direction of the turn or external load applied to the track and by underdriving a similar output shaft located on the same side of the vehicle as the direction of the turn or load. Braking action results when control shafts having mechanical brakes attached and extending outwardly away from the gearbox toward the tracks are made to slow or stop at equal rates of speed by actuating the brakes at each side of the vehicle uniformly.
Steering differentials known in the art have been limited by the requirement that the brakes used to determine the rotational speed of the control shafts be located within the space of the gearbox thereby restricting the access required for servicing and the range of brake types that can be used for various applications. Located within the gearbox, the brakes are susceptible to contamination by the gear lubricant and exposure to the high operating temperature of the system. Where brakes have been located outside the gearbox, their position has necessarily been maintained inboard of the power coupling device that connects the axle drive shaft carrying power to the wheels.
Service failures of the differential cluster gears have been a commonly recurring problem in steering differential units heretofore known because, typically, the cluster gears have been the smallest yet heaviest loaded of the unit. Each cluster runs with a single mating cluster and intermeshes with a single control gear. This arrangement requires that when the cluster set is made to transmit power to the opposite side for steering control or differential action, drive is transmitted at a single meshing contact point on each cluster gear.